名词
中文翻译：Unknown
同义词：
['knuckle-pin cover', 'knuckle-pin case', 'knuckle-pin protector']
例句：
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1. This notebook hasa knuckle-pin cover that keeps the pages securely shut.
这本笔记本有一个扣环式封面，可以安全地关闭页面。
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2. The artist used a knuckle-pin cover to protect his painting from dust and moisture.
艺术家使用了一个扣环式封面来保护他的画作免受灰尘和湿气的影响。
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3. The knuckle-pin cover is designed to keep valuable documents safe while in transit.
扣环式封面被设计成在运输过程中可以保护珍贵文件的安全。